Presence Of Bromide Research Articles

Fabrication of selective electrochemical sensor for the detection of folic acid in spinach, wheat and tablets using functionalized graphene-oxide based molecular imprinted polymer

A novel cost-effective sensor material was developed from modified graphene oxide based molecular imprinted polymer (GO-MIP) for the detection of folic acid (FA). This GO-MIP was obtained through several processes including functionalization, polymerization and template molecule introduction/removal during the synthesizing process. Firstly, graphene oxide (GO) was prepared by modified Hummers method which undergoes hydroxyl functionalization to form GO–OH. It further undergoes surface modification with allyl bromide in presence of sodium hydroxide (NaOH) and dimethyl sulfoxide (DMSO) to form vinylated GO–OH (GO–O–CH=CH2). The GO–O–CH=CH2 subjected to further molecular imprinting process with methacrylic acid (MAA) as the monomer and ethylene glycol dimethacrylate (EGDMA) as the cross-linker, azobisisobutyronitrile (AIBN) as the initiator and FA as the template molecule. The different preparatory stages of materials were characterized by FTIR, XRD and SEM techniques to understand the formation. The obtained GO–MIP was used as an active material for FA sensing. The pH studies were carried out using cyclic voltameteric measurement and maximum current is obtained at pH 4.0. The proposed GO-MIP based electrode showed excellent electrocatalytic activity toward FA detection at optimized conditions. The limit of detection obtained in the present study is 1.0 nM. The results obtained from the real time usability of electrodes in wheat flour, tablet and spinach are well with commercially available FA monitors. The results endorse the promising application of GO-MIP toward superior FA sensing with long-term stability.

Kinetic and mechanistic study of the effect of Cu(II) on monochloramine stability in bromide-containing waters

Naturally occurring bromide can reduce the stability of monochloramine (NH2Cl) by forming brominated halamines, the most abundant being bromochloramine (NHBrCl). Cu(II) is found in drinking water distribution systems from copper pipes leaching or added as a biocide. This study showed that Cu(II) can catalyse the decay of NHBrCl (proved by Membrane Introduction Mass Spectrometry) during the chloramination process. 11 % of the total oxidant (chloramines, bromamines and NHBrCl) was consumed during chloramination in bromide-containing waters at pH 6.5 after 6 h, while the presence of Cu(II) remarkably accelerated the total oxidant decay with 65 % consumption. Higher bromide concentrations and lower pH led to an increasing total oxidant decomposition. This was primarily ascribed to the higher formation of NHBrCl and its further catalytic degradation from Cu(II) under these conditions. The nitrogen by-products in the presence of bromide and Cu(II) were identified. Nitrogen gas and ammonia were shown to be the main degradation products and a mechanism involving NHBrCl decomposition is proposed. It was also verified that Cu(II) enhanced the disinfectant decay in the absence/presence of bromide when natural organic matter was present. These findings can provide useful information to water utilities to better manage and maintain the stability of disinfectant residual allowing safe distribution of drinking water over a wide geographical area.

Disinfection of bromide-containing tryptophan water by UV/chlorine: brominated halonitromethane formation, impact factors, and pathways

Tryptophan was selected as the precursor for the investigation on the formation of brominated halonitromethanes (Br-HNMs) in the presence of bromide during UV/chlorine disinfection.

The influence of bromide and iodide ions on the sulfamethoxazole (SMX) halogenation during chlorination

Disinfection by-products (DBPs) were produced during the chlorination process, posing a threat to drinking water safety and human health. In the presence of bromide and iodide ions, brominated and iodinated DBPs will be generated, which might be more toxic than the parent compound. However, there are few studies on brominated and iodinated DBPs of antibiotics. Therefore, in this study, the fates of sulfamethoxazole (SMX) during chlorination in different systems (Blank; SMX + NaClO; SMX+ NaClO+ Br−; SMX+ NaClO+I−; SMX+ NaClO+ Br− + I−) were investigated. In different systems, all the reaction followed a pseudo-first-order kinetics, while the reaction rates of NaClO with SMX were different, the reaction rates were in order of SMX + NaClO + Br− + I− > SMX + NaClO + Br− > SMX + NaClO + I− > SMX + NaClO. When Br− and I− existed simultaneously, the reaction rate was the fastest. Iodide played an important role in oxidation and promoted the chlorination of SMX. SMX mainly underwent S-C cleavage, S-N hydrolysis, desulfonation, and substitution reactions. Nine disinfection by-products, including three reported for the first time, were identified using a non-targeted approach, and degradation pathways were proposed. Furthermore, EPI Suite software was applied to predict the environmental accumulation potential and environmental persistence of the degradation products. The results indicated that SMX and degradation products had little environmental accumulative potential and environmental persistence.

Presence of bromide and iodide promotes the horizontal transfer of antibiotic resistance genes during chlorination: A preliminary study

Chlorination was reported to have a great potential to increase horizontal gene transfer (HGT) of antibiotic resistance genes (ARGs), which poses a great threat to global human health. Bromide (Br−) and iodide (I−) ions are widely spread ions in water and wastewater. In chlorination, Br− and I− can be oxidized to active bromine and iodine species. The influence of the co-existing different halogen oxidants (chlorine + bromine or iodine species) on HGT of ARGs were rarely investigated. In this study, the conjugative transfer of ARGs between a donor strain E. coli K12 and a recipient strain E. coli HB101 was investigated in chlorination without/with the presence of Br− or I−. Immediately after the addition of sodium hypochlorite, 53–88 % of the dosed chlorine was rapidly consumed, 10 %–42 % fast transformed into organic combined chloramines, and only low levels of free chlorine (0.02–0.8 mg/L as Cl2) left in the diluted cultural medium. Conjugative transfer mediated by the RP4 plasmid was not significantly enhanced in chlorination without the presence of Br− or I−. With the presence of Br− (0.5–5.0 mg/L) or I− (0.05–0.5 mg/L) in chlorination, the co-existing free halogen oxidants and their organic combined ones up-regulated the mRNA expression of the oxidative stress-regulatory gene (rpoS), outer membrane protein gene (ompC), and conjugation-relevant genes (trbBp and trfAp), and caused more damage to cell entirety. As a result, the co-existing reactive halogen oxidants enhanced the HGT of ARGs probably via conjugative transfer and transformation. This study showed that the presence of Br− and I− of common levels in aquatic environment promoted HGT of ARGs in chlorination, thus accelerating the transmission and prevalence of ARGs.

Degradation pathways and kinetics of chloroacetonitriles by UV/persulfate in the presence of bromide

Chloroacetonitriles (CANs) are highly toxic nitrogenous disinfection by-products (N-DBPs), which frequently appear in water supply systems and have attracted widespread attention. UV/persulfate (PS) is an effective method to degrade CANs. Bromide (Br−) is widespread in aquatic environments and reacts with oxidative radicals to produce secondary reactive bromine species (RBS), which affects the degradation of CANs by UV/PS. It was found that the degradation of CANs was highly inhibited by Br−. The apparent first-order reaction rate constants of monochloroacetonitrile (MCAN), dichloroacetonitrile (DCAN) and trichloroacetonitrile (TCAN) decreased from 2.63 × 10−3, 2.00 × 10−3 and 8.66 × 10−4 s−1 to 2.58 × 10−4, 1.61 × 10−4 and 1.59 × 10−4 s−1, respectively after adding 20 μM of Br−. HO• was the main radicals contributing to the degradation of CANs when the concentration of Br− was less than 10 μM, compared with SO4•− and direct photolysis. When the concentration of Br− was up to 20 μM, the contributions of RBS accounted for 85.7%, 90.7% and 89.9% of the apparent degradation rate constants of CANs, respectively. During the reaction, about 65% of nitrogen atoms were transformed into NO3− by the CC bond cleavage and oxidation. The yields of Cl− by dechlorination reaction accounted for 83.5%, 71.0% and 41.2% of the chlorine contents in MCAN, DCAN and TCAN, respectively. It was verified that CANs react with free bromine (HOBr) to produce bromochloroacetonitrile (BCAN). DCAN and TCAN are hydrolyzed to produce corresponding haloacetamides (HAMs), which are further reacted with HOBr to produce bromodichloroacetic acid (BDCAA). Furthermore, the generation of bromate was also worth noting via the oxidation of Br− in the UV/PS system.

Removal of disinfection byproducts and toxicity of chlorinated water by post-treatments of ultraviolet/hydrogen peroxide and ultraviolet /peroxymonosulfate

Post-treatment of ultraviolet (UV) irradiation is not efficient in eliminating toxicity of chlorinated water. Removal of disinfection byproducts (DBPs) and toxicity of chlorinated water by UV/hydrogen peroxide (UV/H2O2) and UV/peroxymonosulfate (UV/PMS) was investigated. In the absence of bromide, adding H2O2 or PMS enhanced the removal of nitrogenous DBPs and total organic chlorine (TOCl) than UV alone (1200 mJ/cm2). UV/PMS decreased the cytotoxicity from 10.6 to 4.4 mg-Phenol/L and genotoxicity from 7.1 to 2.0 μg-4-NQO/L, more efficient than UV/H2O2. However, results were quite different in the presence of bromide. PMS led to the increased formation of total organic bromine (TOBr) in chlorinated water. UV/PMS was therefore less efficient in toxicity removal than UV/H2O2. In the presence of bromide, UV/H2O2 decreased the cytotoxicity and genotoxicity by 85% and 68%, while UV/PMS only removed the cytotoxicity and genotoxicity by 59% and 46%. In the UV/PMS process, SO4˙- was more efficient on toxicity removal than ˙OH. Contributions of UV irradiation, ˙OH and SO4˙- were 55%, 14% and 31% to cytotoxicity removal, and 49%, 15% and 36% to genotoxicity removal. This study demonstrated the feasibility of using UV/H2O2 and UV/PMS as post-treatments to enhance the removal of DBPs and toxicity of chlorinated water.

Brominated trihalamines in chlorinated seawaters: Quantification of tribromamine and identification of bromochloramines by Membrane Introduction Mass Spectrometry

During chlorination of seawater, the presence of bromide and ammonia alters the speciation of the oxidant and lead to the formation of chlorinated and brominated amines. This can affect the effectiveness of the disinfection treatment and the formation of disinfection by-products released to the environment. In this study, a Membrane Introduction Mass Spectrometry (MIMS) analytical method was developed to differentiate brominated trihalamines (i.e. tribromamine NBr3, dibromochloramine NBr2Cl and bromodichloramine NBrCl2) in synthetic and natural chlorinated seawater. A mass-to-charge ratio of m/z = 253 corresponding to the parent ion was used for the quantification of NBr3 in absence of organic matter and the signal of the fragment at m/z = 177 was chosen in presence of high concentration of organic matter. Limits of detection were 0.23 μM (49 μg Cl2/L) and 0.18 μM (38 μg Cl2/L) for m/z 253 and m/z 177, respectively. Both NBr2Cl and NBrCl2 were monitored in chlorinated seawaters with their respective parent ion at m/z = 207 and m/z = 163 but were not quantified. MIMS results also showed that reaction of brominated trihalamines with natural organic matter (NOM) was a minor pathway for 1–2 mg C/L compared to their auto-decomposition in natural or synthetic seawater. Overall, MIMS was able to unambiguously differentiate and monitor brominated trihalamines for the first time in chlorinated seawater, which was not possible by using UV measurement, titration and colorimetric methods.

Degradation of bisphenol A by UV/persulfate process in the presence of bromide: Role of reactive bromine

Bromide (Br−), a ubiquitous species in natural water, is capable of reacting with sulfate radical (SO4∙−) and hydroxyl radical (∙OH) to form secondary reactive bromine species (RBS). The reaction routes can influence the degradation mechanisms and performance of these radicals for removal of target pollutants and may also form harmful bromine-containing disinfection by-products (Br-DBPs) during subsequent chlorination. In the present research, the UV-activated persulfate (PS) degradation of bisphenol A (BPA) was systematically examined in the presence of Br−. Results indicated that the presence of Br−enhanced the BPA degradation and both UV/PS and UV/PS/Br− processes followed the pseudo-first-order kinetics. At 0–0.8 mM Br−, 0.2 mM Br− exerted the best enhanced effect on BPA degradation, while RBS functioned as the major contributor in the presence of 0.05–0.5 mM Br−. Solution pH (6.0–8.0) barely affected the BPA degradation in the UV/PS system, but the introduction of Br− augmented the pH dependence. In the UV/PS/Br−system, the reaction rate constant of BPA increased/decreased with increasing PS/HA dosage, and was affected slightly in the presence of bicarbonate and chloride. According to the quantum chemical calculation, the second-order rate constants of BPA with ∙OH, SO4∙−, Br∙ and Br2∙− were calculated as 7.65 × 1010, 1.67 × 109, 1.77 × 108 and 2.83 × 102 M−1 s−1, respectively. Additionally, three degradation pathways of BPA were proposed based on DFT calculation and HPLC/MS analysis, and the formed bromine-containing products exhibited higher toxicity than BPA. Br-DBPs, particularly tribromomethane and tribromoacetic acid, generated from UV/PS/Br−pre-oxidation during BPA chlorination significantly increased the toxicity of total DBPs.

Comparison of UV and UV/chlorine system on degradation of 2,4-diaminobutyric acid and formation of disinfection byproducts in subsequent chlorination

• UV/chlorine system showed extremely excellent performance in degrading DAB. • C-C bond and C-N bond fracture were the main reactions of DAB degradation by UV. • RCS produced by UV/chlorine system preferentially attacked amino groups on DAB. • N-DBPs had great formation potential when UV/chlorine was used as pretreatment. • THMs were more prone to bromine substitution than HANs. 2,4-diaminobutyric acid (DAB) is a common non-protein amino acid with extremely high neurotoxicity in water environment, posing a serious threat to human health and animal welfare around the world. Therefore, it is necessary to take appropriate measures to remove it. In this paper, degradation of DAB in UV and UV/chlorine system were studied, and transformation pathways of DAB were preliminarily proposed based on the identified transformation products. Moreover, formation of disinfection byproducts (DBPs) during post-chlorination under different conditions were also discussed. The results indicated that the presence of reactive substances in UV/chlorine system significantly promoted the degradation of DAB, but more DBPs and their precursors were produced at the same time. UV irradiation time, pH and Cl 2 /N affected the formation of DBPs during post-chlorination to various degrees. Notably, precursors of carbonaceous DBPs were mainly formed during UV irradiation, while those of nitrogenous DBPs were mainly formed during UV/chlorine system. In the presence of bromide, brominated DBPs were the absolute dominant species, while formation of chlorinated DBPs were inhibited. Furthermore, total trihalomethane and total haloacetonitrile increased with increasing bromide concentration. Overall, special attention should be paid to DBP formation when selecting UV or UV/chlorine system as pretreatment to eliminate DAB.

Sequential injection spectrophotometric method for screening bromate produced as an ozonation water disinfection by-product.

The aim of this work was the development of an automatic sequential injection analysis method to monitor the ozonation process for water disinfection. The determination was based on the reaction between bromate and o-dianisidine in the presence of bromide in acidic medium. The determination parameters were studied and adjusted to enable bromate quantification in the range 0.35-4.0mg BrO3-/L with a limit of detection of 20μg BrO3-/L. The choice of a sequential injection procedure enabled a minimal consumption of reagents and no need for sample pre-treatment. The developed sequential injection proved to be accurate with < 5% relative deviation when compared to ICP-MS and an average of 101% in recovery percentages studies. It was effectively applied to monitor an ozonation process enabling the follow-up of the process with real-time quantification of the bromate content.

Preferential Halogenation of Algal Organic Matter by Iodine over Chlorine and Bromine: Formation of Disinfection Byproducts and Correlation with Toxicity of Disinfected Waters.

The increasing occurrence of harmful algal blooms (HABs) in surface waters may increase the input of algal organic matter (AOM) in drinking water. The formation of halogenated disinfection byproducts (DBPs) during combined chlorination and chloramination of AOM and natural organic matter (NOM) in the presence of bromide and iodide and haloform formation during halogenation of model compounds were studied. Results indicated that haloform/halogen consumption ratios of halogens reacting with amino acids (representing proteins present in AOM) follow the order iodine > bromine > chlorine, with ratios for iodine generally 1-2 orders of magnitude greater than those for chlorine (0.19-2.83 vs 0.01-0.16%). This indicates that iodine is a better halogenating agent than chlorine and bromine. In contrast, chlorine or bromine shows higher ratios for phenols (representing the phenolic structure of humic substances present in NOM). Consistent with these observations, chloramination of AOM extracted from Microcystis aeruginosa in the presence of iodide produced 3 times greater iodinated trihalomethanes than those from Suwannee River NOM isolate. Cytotoxicity and genotoxicity of disinfected algal-impacted waters evaluated by Chinese hamster ovary cell bioassays both follow the order chloramination > prechlorination-chloramination > chlorination. This trend is in contrast to additive toxicity calculations based on the concentrations of measured DBPs since some toxic iodinated DBPs were not identified and quantified, suggesting the necessity of experimentally analyzing the toxicity of disinfected waters. During seasonal HAB events, disinfection practices warrant optimization for iodide-enriched waters to reduce the toxicity of finished waters.

Inhibition of bromate formation in the ozone/peroxymonosulfate process by ammonia, ammonia-chlorine and chlorine-ammonia pretreatment: Comparisons with ozone alone

The ozone/peroxymonosulfate (O3/PMS) process, generating hydroxyl radicals (HO•) and sulfate radicals (SO4•-), can effectively remove organic contaminants in water, while forming a remarkable amount of bromate (BrO3-) in the presence of bromide (Br-). This paper firstly investigated the ammonia (NH3), chlorine-ammonia (Cl2-NH3) and ammonia-chlorine (NH3-Cl2) pretreatment in inhibiting BrO3- generation in O3/PMS process at different conditions, and the inhibition degree was compared with O3 alone. All the three kinds of pretreatment at Cl2 and NH3 dosages of 50 and 100 mM reduced 90 % or more of the overall BrO3- formation, while the NH3-Cl2 pretreatment strategy is prior to that of the NH3 and Cl2-NH3. The inhibition degree of the pretreatment strategies under different pH were: 5.0 > 9.0 > 7.0 > 3.0. Meanwhile, the inhibition degree increased as the initial Br- concentration increased from 15 to 50 µM. After each pretreatment strategy, there was a higher BrO3- inhibition efficiency accompanied with a lower ozone utilization efficiency in O3 alone than that of O3/PMS process. Furthermore, the mechanism of BrO3- inhibition by the pretreatment strategies was also clarified. The main products produced by masking Br- in the NH3-Cl2 pretreatment were more difficult to regenerate Br-, as a result, the NH3-Cl2 pretreatment strategy produced the least BrO3- among the three kinds of pretreatment strategies. Finally, compared with the deionized water, the pretreatment strategies shown better inhibition performance in actual water because the water matrices would trap free radicals and HOBr to reduce BrO3- formation. At the same time, the NH3-Cl2 pretreatment strategy generated fewer disinfection by-products than that of Cl2-NH3 pretreatment in actual water. Therefore, the NH3-Cl2 pretreatment strategy is a practical way to control the BrO3- formation in the O3/PMS process.

Integration of fluorescence quenching correction into trihalomethane formation prediction models.

Despite there being numerous models of trihalomethane (THM) formation, they are limited by high estimation errors, which can be close to the regulatory limits for THMs, due to the fluorescence quenching effect. In this research, the estimation error for THM formation was reduced by correcting the quenching effect. The trihalomethane formation potential (THMFP) test was conducted in the presence of chlorine and bromine, individually and in mixtures. The THM precursors used in this study were protein (bovine serum albumin; BSA), amino acids (tryptophan and tyrosine), chlorine, bromine, and Suwannee River natural organic matter (SWNOM). BSA tended to form bromodichloromethane (BDCM) rather than trichloromethane (TCM) during chlorination in the presence of bromide (Br-). In contrast, SWNOM tended to form chlorinated THMs (TCM) rather than brominated THMs (BDCM and dibromochloromethane; DBCM), and no TBMs were formed in these processes. BSA with SWNOM decreased the formation of TCM due to the decrease in the amount of TCM precursor in SWNOM through binding with BSA. The concentration of each THM species was predicted from the fluorescence intensity of peak C, corrected fluorescence intensity of peak T, and Br- concentration. The use of humic-like and corrected protein-like fluorescence in the excitation-emission matrix model for predicting THM species reduced the prediction error. In this research, correction of the fluorescence quenching decreased the mean percentage estimation error for TCM, BDCM, and DBCM from 47%, 35%, and > 100% in classical approaches to 6.6%, 26.9%, and 2.0%, respectively. This study is expected to make contributions in reporting the relationship between the concentration of natural organic matter compositions and the formation of THM species.

Formation and transformation of halonitromethanes from dimethylamine in the presence of bromide during the UV/chlorine disinfection

Halonitromethanes (HNMs) is a typical class of nitrogenous disinfection byproducts with high toxicity. The effect of Br− on the formation and transformation of HNMs from dimethylamine (DMA) during the ultraviolet (UV)/chlorine disinfection has been investigated in current study. Results reveal that only chloronitromethane, dichloronitromethane and trichloronitromethane (TCNM) could be found during the UV/chlorine disinfection. Whereas in the presence of Br−, nine species of HNMs could be observed simultaneously. When Br− concentration increased from 0 to 15.0 mg L−1, the predominant species of HNMs were gradually changed from TCNM to dibromonitromethane and tribromonitromethane, which contributed to 23.37% and 31.07% of total HNMs concentration at 15 mg L−1 Br−, respectively. The presence of Br− not only shifted the chlorinated-HNMs (Cl-HNMs) towards brominated-HNMs (Br-HNMs) but also affected the dominant species and total concentration of HNMs. When Br− concentration was 4.0 mg L−1, the formation of HNMs decreased with the increase of pH from 6.0 to 8.0 and increased with the increase of free chlorine and DMA. When free chlorine concentration rose from 0.25 to 1.1 mmol L−1, Br-HNMs were shifted to Br(Cl)-HNMs and then to Cl-HNMs. According to the findings, possible formation and transformation pathways of HNMs from DMA were proposed in the presence of Br− during the UV/chlorine disinfection. Finally, it was proved that the effect of Br− on the trend of HNMs in real water was similar to that in deionized water, but higher HNMs concentrations and delayed peak time were observed in real water. This study can provide the scientific evidence and fundamental data for the applications of UV/chlorine disinfection in the treatment of water containing Br−.

Kinetics of diatrizoate degradation by ozone and the formation of disinfection by-products in the sequential chlorination

Abstract In this study, we studied the degradation kinetics of a common iodine contrast agent, diatrizoate, by ozone and the formation of disinfection by-products (DBPs) in the sequential chlorination. Effects of ozone concentration, solution pH, and bromide concentration on diatrizoate degradation were evaluated. The results indicate that diatrizoate can be effectively degraded (over 80% within 1 h) by ozone, and the degradation kinetics can be well described using the pseudo-first-order kinetic model. The pseudo-first-order rate constant (kobs) of diatrizoate degradation significantly increased with increasing ozone concentration and decreasing bromide concentration. The kobs kept increasing with the increase of pH value and reached a maximum of 6.5 (±0.05) × 10−2 min−1 at pH 9. As the ozone concentration gradually increased from 0.342 to 1.316 mg/L, the corresponding kobs of diatrizoate degradation increased from 1.76 (±0.20) × 10−3 to 4.22 (±0.3) × 10−2 min−1. The bromide concentration exhibited a strong inhibitory effect on diatrizoate degradation because of the competition for ozone with diatrizoate. Trichloromethane was the only detected DBP in the subsequent chlorination in the absence of bromide. However, in the presence of bromide, six other DBPs were detected, and bromochloroiodomethane and tribromomethane became the major products with concentrations 1–2 orders higher than those of the other DBPs. In order to provide safe drinking water to the public, water should be maintained at circumneutral pH values and low bromine concentrations (&amp;lt;5 μM) before reaching the chlorine disinfection process to effectively control the formation of DBPs.

Mechanistic and kinetic understanding of micropollutant degradation by the UV/NH2Cl process in simulated drinking water

The UV/monochloramine (UV/NH2Cl) process has attracted increasing attention in water treatment, in which hydroxyl radicals (HO•), reactive chlorine species (RCS) and reactive nitrogen species (RNS) are produced. This study investigated the effects of water matrices including halides, natural organic matter (NOM), alkalinity and pH, on the degradation kinetic of a variety of micropollutants and radical chemistry in the UV/NH2Cl process. The presence of chloride blunted HO• and Cl• impacts, but enhanced Cl2•- effect on micropollutants reactive toward Cl2•-. The presence of 30 μM bromide led to an 82% decrease in the specific pseudo-first-order rate constants (k') by HO• (kHO•'), and significantly diminished RCS efficacy. Reactive bromine species (RBS) were formed in the presence of bromide, while the contribution could not compensate for the decrease of HO• and RCS due to their lower reactivity toward micropollutants. Iodide rapidly transformed to HOI via reacting with NH2Cl, which resulted in a 59% decrease of kHO•' and 12% ∼ 100% decreases of k' by reactive halogen species (RHS) and RNS (kRHS+RNS') for most micropollutants. Nevertheless, k' of phenolic compounds, such as paracetamol, bisphenol A and salbutamol, increased in the presence of iodide by 78%, 360% and 130%, respectively, due to the roles of HOI and reactive iodine species (RIS). Bicarbonate decreased the contributions of HO• and RCS, but enhanced that of CO3•- for micropollutants reactive toward CO3•-. The presence of 1 mg/L NOM scavenged over half the amount of HO•, and also consumed RCS and RNS, resulting in significantly decreased removal of micropollutants. High pH value witnessed enhanced degradation for those micropollutants reactive toward RCS and RNS through deprotonation. The degradation of most micropollutants was inhibited in real drinking water and in the coexistence of halides. This study provides a better understanding of radical chemistry in the UV/NH2Cl process under a practical water treatment condition.

Formation of organic chloramines during chlorination of 18 compounds

Organic chloramines have attracted considerable attention because of their potential toxicity and reactivity. However, the lack of suitable and effective analytical methods has limited the study of organic chloramines due to their volatile and unstable properties. In this study, membrane introduction mass spectrometry (MIMS) combined with DPD/FAS titration was used to monitor the formation of organic chloramines. N-chlorodimethylamine [(CH3)2NCl] and N-chlorodiethylamine [(C2H5)2NCl] were detected and identified as the dominant volatile DBPs during chlorination of 18 organic compounds with dimethylamine or diethylamine functional groups, with yields ranging from 0.3% to 51.1% at a chlorine to precursor (Cl/P) molar ratio of 8.0. (CH3)2NBr was formed in the presence of bromide, while the formation of (CH3)2NCl was decreased. The reaction of phenol with (CH3)2NCl combined with theoretical calculations confirmed that the reactivity of (CH3)2NCl was similar to that of monochloramine. Moreover, (CH3)2NCl and (C2H5)2NCl were observed at the ppb level during chlorination of actual water samples collected from different areas. The results suggest that (CH3)2NCl and (C2H5)2NCl are important organic chloramines during chlorination, which may lead to the occurrence of further oxidation reactions and promote the formation of other disinfection byproducts simultaneously and should be of concern.

The direct C(sp2)-H functionalization and coupling of aromatic N-heterocycles with (hetero)aryl bromides by [PdX2(imidazolidin-2-ylidene)(Py)] catalysts

In this study, a series of air- and moisture-stable imidazolidin-2-ylidene-based new palladium complexes with the general formula [PdX2(NHC)(Py)] were synthesized (NHC = N-heterocyclic carbene, Py = pyridine, X = Cl or I). The structures of the palladium complexes were characterized by different techniques such as 1H NMR, 13C NMR, FT-IR spectroscopy and elemental analysis. The more detailed structural characterization of one of the palladium complex was determined by single-crystal X-ray diffraction study. The catalytic activities of all palladium complexes were tested in the direct arylation of five-membered aromatic N-heterocycles such as 3,5-dimethylisoxazole and 1-methyl-1H-pyrrole-2-carboxaldehyde with (hetero)aryl bromides in presence of 1 mol% catalyst loading at 120 °C. Desired products were obtained in moderate to good yields.

Toxicity of Ozonated Wastewater to HepG2 Cells: Taking Full Account of Nonvolatile, Volatile, and Inorganic Byproducts.

Wastewater ozonation forms various toxic byproducts, such as aldehydes, bromate, and organic bromine. However, there is currently no clear understanding of the overall toxicity changes in ozonated wastewater because pretreatment with solid phase extraction cannot retain inorganic bromate and volatile aldehydes, yet contributions of known ozonation byproducts to toxicity are unknown. Moreover, compared with bromate, organic bromine did not receive widespread attention. This study evaluated the toxicity of ozonated wastewater by taking aldehydes, bromate, and organic bromine into consideration. In the absence of bromide, formaldehyde contributed 96-97% cytotoxicity and 92-95% genotoxicity to HepG2 cells among the detected known byproducts, while acetaldehyde, propionaldehyde, and glyoxal had little toxicity. Both formaldehyde and dibromoacetonitrile drove toxicity among the known byproducts when bromide was present. Toxicity assays in HepG2 cells showed that when secondary effluents contained no bromide, the cytotoxicity of the nonvolatile organic fraction (NVOF) was reduced by 56-70%, and genotoxicity was completely removed after ozonation. However, the formed aldehydes (volatile organic fraction, VOF) led to increased overall toxicity. In the presence of bromide, compared with the secondary effluent, ozonation increased the cytotoxicity of the NVOFBr from 3.4-4.0 mg phenol/L to 10.3-13.9 mg phenol/L, possibly due to the formation of organic bromine. In addition, considering the toxicity of VOFBr (VOF in the presence of bromide, including aldehydes, tribromomethane, etc.), the overall cytotoxicity and genotoxicity became much higher than those of the secondary effluent. Although bromate had a limited impact on cytotoxicity and genotoxicity, it caused an increase in oxidative stress in HepG2 cells. Therefore, when taking full account of nonvolatile, volatile, and inorganic fractions, ozonation generally increases the toxicity of wastewater.